Who is the founder of advaita?
There is no single founder of advaita. Since the philosophy of advaita is rooted in the upanishads, which are part of the eternal vedas, the advaita tradition does not trace itself to a historical personality. However, SankarAcArya is venerated as the most important teacher of advaita vedAnta, as he wrote commentaries to the basic scriptural texts, and placed the living advaita tradition on a firm footing. Before SankarAcArya’s time, the tradition was passed down mainly through oral instruction. Even today, the traditional way to learn advaita is to sit at the feet of an accomplished guru. Mere reading of the texts is insufficient. More details about the guru paramparA of advaita are at http://www.advaita-vedanta.org/avhp/advaita-parampara.html. There is a description of pre-Sankaran vedAnta at http://www.advaita-vedanta.org/avhp/pre-sankara.html.